The present disclosure relates generally to a well bore servicing fluid, and more particularly to the viscosification of a well bore servicing fluid using polymers comprising betaine units.
In the past, well drilling and development operations have employed large amounts of fresh water. In some areas, obtaining fresh water for these operations has become more expensive and difficult due to water shortages and government regulation. On the other hand, vast amount of produced water can be generated from hydrocarbon wells. Generally, this produced water must be disposed of at a significant cost. Given the volume of fresh water required for well operations, the ability to reclaim and use produced water as a well servicing fluid could alleviate the impact of well operations on fresh water shortages, reduce environmental concerns of contaminating fresh water reserves, and potentially lower the cost of well servicing operations.
However, produced water often has high concentrations of total dissolved solids (“TDS”), including high salinity and hardness content. Many conventional viscosifying polymers, including polyacrylamide based slick water fracturing polymers, do not function well in such high salinity waters, especially in the presence of metals, such as iron, which are often present in produced water. Also, many surfactants commonly used in well servicing fluids have reduced solubility in produced water due to the high TDS content. Reduced solubility of the surfactants can increase mixing times and/or reduce the viscosifying effect of the viscosifying polymers in the produced water. It therefore would be an advancement in the art to discover a novel viscosifying system that worked well in produced water, especially in produced water having relatively high TDS content.
The use of polymers comprising betaine units for viscosifying hydrocarbon well fluids was disclosed by D.V. Satyanarayana Gupta et al., in copending U.S. Patent Application Publication No. 2010/0197530 (“the '530 Application”), published on Aug. 5, 2010, the disclosure of which is hereby incorporated by reference in its entirety. The application discloses a servicing fluid for use in natural gas or oil field wells. The well servicing fluid includes an aqueous brine media and a zwitterionic polymer. The zwitterionic polymer is prepared by polymerization of at least one monomer, Ab, comprising a betaine group and optionally one or more nonionic monomers, Ba. The brines used in the examples of the '530 application were stock completion brines, which are high purity brines and mixtures without significant amounts of contaminants such as iron, barium, strontium, sulfates and other contaminants that are often contained in produced water.
The zwitterionic polymers of the '530 Application may be mixed with brines using a batch mixing process. For examples, the brines can be mixed at high shear with a surfactant, such as ammonium salts of polyarylphenyl ether sulfate in a batch process for about 15 minutes until a desired viscosity of the fluid is reached.
It is well known in the art that well fluid can be mixed “on-the-fly” as it is pumped downhole. On-the-fly processes generally involve mixing components, such as the viscosifying polymer, for a relatively short period of time compared to batch mixing processes, and then pumping the well fluid downhole. In order to mix fluids on the fly, surfactants can be used to allow the viscosifying polymer to mix rapidly and thereby quickly allow the well servicing fluid to reach a suitable viscosity. The ability to mix viscosifying polymers on-the-fly can have certain benefits, including saving time and/or allowing for reduced mixing equipment size and cost relative to batch mixing processes. The ability to employ viscosifying polymers in either batch or on-the-fly mixing processes also increases process flexibility.
Accordingly, there exists a need for improved viscosification agents for use as well bore-servicing fluids that exhibit one or more of the following properties: reduced mixing time, the ability to allow on-the-fly mixing in high salinity water or produced water, good viscosifying power in produced waters, good rheological stability at increased temperatures in produced waters, good stability at a relatively high ionic strength and/or good stability in a relatively saline medium, such as produced water with high total dissolved solids; good thickening power for media comprising a relatively high ionic strength, such as saline media, including highly saline media, and/or a thickening power at low contents of polymer.